<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>

<body>
  <script>
    function foo() {
      console.log(this.a)
    }

    function active(fn) {
      fn(); // 真实调用者，为独立调用
    }
    var a = 20;
    var obj = {
      a: 10,
      getA: foo,
      active: active
    }

    // active(obj.getA);
    // obj.active(obj.getA);
  </script>

  <script>
    var n = 'window';
    var object = {
      n: 'object',
      getN: function() {
        return function() {
          return this.n;
        }
      }
    }
    console.log(object.getN()()); // window
  </script>
</body>

</html>